The human insulin analogue HOE 901 was developed to meet the medical need for a long-acting insulin that can be administered as a single daily injection to yield normal or near-normal blood glucose control with a basal insulin profile that is as smooth as possible over a 24-hour period. Such a preparation should provide better control of nocturnal glycemia and fasting blood glucose levels, and a more stable daytime blood glucose profile. The purpose of this study is to compare the efficacy and safety of HOE 901 with those of NPH human insulin. The study will be performed in subjects with type 1 diabetes who are receiving multi-dose insulin therapy with NPH and regular human insulin. The comparison of HOE 901 and NPH human insulin in terms of efficacy will be based on levels of glycohemoglobin (GHb). In addition to this primary objective, blood glucose variability, other indicators of metabolic control, and quality of life will be compared between the two treatment groups. Safety will be assessed by laboratory findings and the analysis of clinical events.